Conventionally, a fluid apparatus such as a pump or a valve is provided with a gland packing which is a shaft seal part. As such a gland packing, a product is used which is configured by twisting or braiding a plurality of bundled yarns. For example, a method disclosed in Patent Literature 1 is known as a method of manufacturing a yarn which can be used in such a gland packing.
As shown in FIG. 12, a yarn 101 which is manufacture by using such a manufacturing method includes a tubular member 103 which is formed by knitting wire material (metal wire) 102, and further includes a plurality of expanded-graphite materials (filler materials) 104 which are formed into a strip-like shape. The yarn 101 is configured by loading the expanded-graphite materials 104 into the tubular member 103 in a state where the longitudinal directions of the expanded-graphite materials 104 are made extending along the axial direction of the tubular member 103.
In the yarn 101, the tubular member 103 is formed by knitting the wire material 102 with a plurality of knitting needles by a predetermined knitting machine. In a step of knitting the member, then, the plurality of knitting needles are configured so as to repeat only a vertical motion at a predetermined position. Therefore, the tubular member 103 has first stitches 105 which are produced in accordance with the thickness of the knitting needles, and second stitches 106 which are produced in accordance with the distance between adjacent ones of the knitting needles.
As also shown in FIG. 13, the second stitches 106 are formed into gaps having an opening area which is larger than opening areas of the first stitches 105 with respect to the circumferential direction of the tubular member 103 (the smaller the number of the knitting needles, the larger the degree by which the second stitches 106 are larger than the first stitches 105). The second stitches 106 have a width (the dimension in the circumferential direction) which is larger than the width (the dimension in the short side direction) of the expanded-graphite materials 104, and are continuously placed so as to be arranged substantially in a row in the axial direction of the tubular member 103.
When the expanded-graphite materials 104 are loaded into the tubular member 103, therefore, the expanded-graphite materials 104 line up along the row of the second stitches 106 which are arranged in the axial direction of the tubular member 103, so that end portions 108 in the long side direction of the expanded-graphite materials 104 are easily exposed as a whole through the second stitches 106 to the outside of the tubular member 103. Consequently, there is a possibility that, in the vicinities of the end portions 108, a part of the expanded-graphite materials 104 easily slips off the tubular member 103 through the second stitches 106.
Furthermore, the tubular member 103 shows a polygonal shape (in the case where the number of the knitting needles is three, a triangular shape) in which a sectional shape perpendicular to the axial direction has an edge portion in the vicinity of the first stitch 105. In the case where a gland packing is configured by using the yarn 101, when a plurality of yarns (including the yarn 101) are crumpled for braiding or the like, therefore, for example, the expanded-graphite materials 104 of the yarn 101 are rubbed with other yarns through the second stitches 106, and therefore easily slip off the tubular member 103.
In the tubular member 103, when stitches (the first stitches 105 and the second stitches 106) which are produced by using the wire material 102 are made as small as possible, slipping of the expanded-graphite materials 104 from the tubular member 103 can be suppressed. When the stitches are simply made as small as possible, however, the rate of the wire material 102 in the tubular member 103 becomes excessively large, and there arises a problem that the manufacturing cost is increased.